Blood in the placenta and umbilical cord after birth Cord blood (umbilical cord blood) is blood that remains in the placenta and in the attached umbilical cord after childbirth. Cord blood is collected because it contains stem cells, which can be used to treat hematopoietic and genetic disorders. Cord blood is composed of all the elements found in whole blood - red blood cells, white blood cells, plasma, platelets.[1] Compared to whole blood some differences in the blood composition exist, for example, cord blood contains higher numbers of natural killer cells, lower absolute number of T-cells and a higher proportion of immature T-cells.[2] However, the interest in cord blood is mostly driven by the observation that cord blood also contains various types of stem and progenitor cells, mostly hematopoietic stem cells.[1][2][3] Some non-hematopoietic stem cell types are also present in cord blood, for example, mesenchymal stem cells, however these are present in much lower numbers that can be found in adult bone marrow.[2][3]Endothelial progenitor cells and multipotent unrestricted adult stem cells can also be found in cord blood.[3] The stem cells found in cord blood are often confused with embryonic stem cells - unlike embryonic stem cells, cord blood stem cells are all types of adult stem cells, are lineage restricted and are not pluripotent.[3][4][5] Cord blood is used the same way that hematopoietic stem cell transplantation is used to reconstitute bone marrow following radiation treatment for various blood cancers, and for various forms of anemia.[6][7] Its efficacy is similar as well.[6] Adverse effects are similar to hematopoietic stem cell transplantation, namely graft-versus-host disease if the cord blood is from a genetically different person, and the risk of severe infection while the immune system is reconstituted.[6] To assure that the smallest amount of complications occur during transplantation, levels of engraftment must be present; specifically both neutrophils and platelets must be being produced.[8] This process of neutrophil and platelet production after the transplant, however, takes much longer than that of stem cells.[8] In many cases, the engraftment time depends on the cell dose, or the amount of stem cells obtained in the sample of blood.[8] In Dr.